High current consumption during RF sending

[Vicnet]

Hi,

1. I would to know why when the DC/DC is enabled the current is very high (57mA) during RF sending.

2. Why at the end of RF sending the current is higher than previously (15.4mA -> 16.5mA) & 12.3mA -> 57mA)

Test conditions:

• nRF51822 - (Insight 130301)

• RF sending every 90ms

• Payload size: 32bytes

• Supply voltage 2.400V

Thanks you

[Vicnet]

Insight SIP confirm that a 4.7µF external capacitor has to be add on VCC to reduce high current peak.

With 4.7µF the peak current is 57mA -> 42mA.

Does it exist another solution to reduce this peak without disable DC/DC?

[Asbjørn]

The additional 4.7 uF was placed outside the module or were you able to actually replace the C9 capacitor on the module itself? The concern is that the capacitor is places too far from the chip and DCDC itself to be able to handle it efficiently on such a small module. From the qualifications we have done on the chip internally we have used larger PCBs where we also place the additional 4.7 uF capacitor right next to the chip.

[Vicnet]

It was placed outside the module. Maybe to far from the module.

[Asbjørn]

It seems like the capacitor had some effect on the peak, but I do suspect that the distance from the chip and also the overall size of the module would require the capacitor to have a different valuer or potentially a different combination of capacitors to reduce the peak. We haven't tested or qualified this module ourselves, so I'm not able to give you hard recommendations from the top of my head. I would recommend you, if you are able to, try a few different capacitor values, probably with higher value. This in combination with asking Insight SIP if they have tried this themselves on their module. They might have better suggestions for that specific module.